Cons of virtualization

So now that we have covered the benefits of virtualization let’s discuss about potential problems that we might face with the technology.

 

Potential single point of failure

This is one of the most underestimated topic when companies think their virtualization projects.

With the added complexity of virtualization and the consolidation of resources if one system fails it’s more complex than with traditional systems.

If a storage system went down on a traditional environment only the servers that were accessing the data on the system fails. With virtualization it’s more common that if a storage system fails lots of virtual machines will be gone.

Same applies for networks on a virtualized environment.

 

Resource contention

 

As with network traffic congestion, resource contention can occur on a physical node if one virtual server spikes consuming hardware resources. If one of your physical servers start running out of hardware resources like memory or CPU power all the virtual machines that run on it will start to under-perform.

 

There are several options that will help you solve this like vmware Dynamic Resource Scheduller (DRS) that allows to perform a load balance of the virtual servers.

 

Increased administrative overhead

This point shouldn’t be taken literally. I believe that is not an increased administrative overhead it’s just the environment went more complex than before with virtualization in place.

Things are easy to manage but when a problem occurs it’s harder to troubleshoot and more experience is required.

 

Complex administration

With virtualization your IT environment gets more complex and there’s no doubt about it. It’s because you need to start using advanced servers, storage and networks.

Also the configuration of the environment gets complex as you need to start mitigating points of failure, increasing availability and maintaining SLAs.

 

High initial investment

As showed before you need to use more expensive equipment and provide yourself with licenses for your virtualization environment. Depending on your IT requirements those could be very expensive and you need to address your budget in order to realize if the organisation can afford it.

Also if you the staff is not well trained on the technology a consultancy might be needed as well. 

 

Training personnel costs

Staff training is as important as the equipment. In order to setup, manage and troubleshoot the virtualization  environment some training is required. Server virtualization involves several technologies so if the IT team of the organization is small and concentrated on a few people those will have to get trained and lots of new knowledge developed.

Some training I believe is required are on the virtualization technology itself, the type of servers that will be used, networks and storage.

Setting up a virtualization environment is not hard if you know what you are doing but it needs to be well setup upfront otherwise troubleshooting or modifying the configuration could be an uphill journey.

 

Increased network traffic within a single node

The network traffic of the virtualized servers also gets consolidated on a single node or server. Network requirements should be analyzed deeply to avoid network congestions. Several options are in place to reduce potential problems like using faster ports and NIC teaming.

Again, you will need reliable ports on the network side to avoid potential problems. Those ports needs to be, at least, redundant.

 

Increase mean time between failure

Because of the complexity added to the environment troubleshooting an issue of a virtualization infrastructure takes more time than it used to on a physical environment.

The stack to troubleshoot is taller than on a physical server and should the analysis should be from bottom to top:

  • GuestApplication
  • Guest operative system
  • Virtual machine
  • Virtualization Layer
  • Physical server
  • Networks (ethernet – storage)

If the virtual environment is running vmware technologies vcenter operations improves troubleshooting tasks with practical information that helps IT administrator find the issue and a possible solution.

 

 

Security

There are several security points that needs to be covered. Security is very important on a virtual environment because if one host gets compromised several virtual machines could be affected.

  • VM escaping is a process that runs on a virtual machine but allows an attacker to gain control of the host were the vm is running. Check with the vendor of the virtualization solution how to mitigate this.
  • DoS Denial of service in the past some technologies like vmware HA needed external services (DNS servers and default gateway) in order to work properly. If an attacker could configure the IP address of the services on other devices a DoS occurred. Today virtualization technology vendors are working to eliminate this kind of external requirements.
  • Shared resources (hardware) because all the hardware resources are shared among each virtual machine if an attacker gains access to the configuration service it could change some configurations  that will impact on the performance of the vms that runs on that host.

This post belongs to Explain the purpose and applitaton of virtualization technology